The invention relates to a method for estimating the sum of the stator and rotor resistances of an induction machine. More specifically, the invention relates to a method, which can be used to estimate the sum of said resistances during the DC-magnetization period of the induction machine.
In a plurality of control methods, the essential parameters of the induction machine are needed for reliable and accurate control. These required parameters include inductances and resistances of the machine. Resistance values are needed in control methods that use tachometer and also in drives without a tachometer. In drives without a tachometer, the importance of rotor resistance estimate depends greatly on the method by which the flux of the machine is estimated. The induction machine manufacturer also gives some estimates for the rotor resistance either directly or indirectly, but these values are known to be somewhat inaccurate for reliable control.
The measurement of stator resistance is easily accomplished, but since the stator and the rotor have no galvanic connection between them, the measurement of rotor resistance is not a straightforward operation. There are multiple known methods for estimation of the rotor resistance either on-line or off-line. One on-line method is presented in Atkinson D. J., Finch J. W, and Acarnley P. P., 1996 “Estimation of rotor resistance in induction motors”, IEE Proceedings on Electrical power Applications, vol. 143, no. 1, pp. 87-94.
However, finding a reliable estimate for rotor resistance has appeared to be a difficult task.